1. Field of the Invention
This invention relates to the treatment of refinery sludges in a closed integrated system utilizing refinery-generated solvents and recycling solvent and oil removed from the sludge back to the refinery for further processing leaving a residue of filtered solids which can be disposed of in a land fill.
2. Description of the Related Art
Refinery sludges are generated during refining operations at various stages in the process of refining crude petroleum oils to finished products. Refinery oily sludges containing entrained oil may be found for example in heat exchanger bundle cleaning solids, leaded or unleaded tank bottoms, slop oil emulsion solids and API separator sludge. These sludges have been defined by the U.S. Environmental Protection Agency (EPA) as Listed Hazardous Wastes. As such, these wastes must be disposed of as a hazardous waste unless firstly, they are treated to meet EPA land disposal treatment standards and, secondly, a petition to delist the particular waste is approved by the EPA. In the past, one acceptable method of disposal of such oil-entrained refinery solids has been incineration. However, incineration is an expensive process that does not recover the entrained oil for recycle to refineries. Thus treatment of refinery sludge for the recovery of oil and separation of solids has long been considered a desirable but yet unattainable alternative.
In particular, a process has long been sought to treat oily sludges to produce an oil portion that can be further treated to produce a saleable product and a solid portion that can be disposed of in a non-hazardous solid waste landfill. To allow such disposal, the solids must meet the EPA's Treatment Standards for Land Disposal, generally based on contaminant concentrations achieved by the Best Demonstrated Available Technology (BDAT), and Toxicity Characteristic Leach Procedure (TCLP) standards for disposal in a hazardous landfill site and must be delisted by the EPA. Upon delisting, the solids must then meet standards set by the particular State for disposal in non-hazardous solid waste landfills in their forum. This means of disposal, in a non-hazardous solid waste landfill as opposed to hazardous waste landfill, is the lowest cost method but has heretofore either not been achievable or has been achievable only with such high sludge processing cost as to be uneconomical.
U.S. Pat. No. 4,260,489 of Greil is directed to the treatment of oily sludge utilizing precoated surface filters such as plate, leaf and tube or candle filters preferably operated under pressure. In such filters, the precoat is effectively the filter medium and the function of the plate, leaf and tube or candle filter is to act as a support. The filter is precoated with diatomaceous earth. The sludge is slurried with water and then passed through the filter to produce a filter cake comprising mainly solid particles together with some oil and water. The filter cake is washed while on the filter with a light hydrocarbon solvent, kerosene or naphtha, to remove the oil and water. Subsequently, steam is applied to the filter cake to remove the solvent. However, the '489 patent teaches that the addition of water prior to filtration is an essential step. As will be explained below, the present invention finds this step deleterious and unnecessary. Additionally, the types of filters used in the '489 patent process all inevitably expose the workers and the surrounding environment to the filter cake and any volatile matter in the filter vessel during the process of removing the cake from the filter and disposing of the cake. In view of the potential for exposure to hazardous materials, it is desirable to operate such a treatment system in an entirely enclosed environment, if possible. United Kingdom Patent 1,535,516 discloses a treatment substantially similar to that of the '489 patent but once again all examples of the '56 UK patent teach that the sludge is slurried with water prior to filtration.
Solvent extraction for treatment of refinery sludge is also disclosed in the oil and Gas Journal article of Vol. 89, No. 1, pp. 73-77. In this oil and Gas Journal article, there is no mention of adding water to the sludge prior to filtration. The sludge is treated with propane as the sole solvent or with propane and then reformate to remove entrained oil. The Oil and Gas Journal article teaches the use of three separate vessel, one for mechanical treatment, one for solvent extraction and one for fixation of the sludge to reduce the leachability of metals in the extracted sludge by the addition of fixation agents such as pozzalonic reactions to immobilize metals and other constituents in the product residue and thereafter dewatering the mixture in a conventional filter press. The Oil and Gas Journal article further teaches that used solvents can be recycled back to the refinery and that facilitates may be added to recover and recycle the solvents within the extraction system. There is no teaching of the utilization of a filter process in which the filter vessel remains fully closed during the filtration process and that does not expose workers or the environment to the contents of the vessel.
U.S. Pat. No. 4,954,267 of Uremovich discloses a process for separating water and gasoline from the solids of a gasoline product tank sludge to produce a filtered, finished gasoline product. Filter aid and sludge are mixed in a mixer assembly and thereafter the mixed sludge and filter aid is pumped through one of a plurality of alternately selectable, sealed, horizontal plate filters. The filtered liquid is recirculated back through the mixing tank until a desired clarity is reached. The clear filtered liquid is then rerouted and pumped to an oil/water separator. The filtrate or cake collected on the filter plate is dried, preferably by introduction of an inert gas, and removed to a disposal site. The patent recommends the use of a Sparkler-brand filter provided with R-17 size nylon filter paper as its preferred filter. The process is operated on a batch basis and the filter plates must be removed and scraped clean between operations, thus exposing workers to potential hazards and exposing the environment to the contents of the filter vessel. The Uremovich patent does not disclose the use of a solvent nor does it disclose the use of steam to remove volatiles from the filter residue, rather, the Uremovich patent relies solely on a filter aid, such as diatomaceous earth, to enhance the filter process.
U.S. Pat. No. 5,092,983 is directed to a method for separating organic material from refinery sludges using solvent extraction techniques. In an optional pretreatment step, the refinery sludge is treated to remove some of the water and organic liquid (oil) from the sludge before treatment with the '983 patent's process. In one embodiment of the invention, most preferably at least about 90% by weight of the free water in the refinery sludge is removed during the pretreatment step. Further, in this pretreatment step, the refinery sludge may be mixed with a filter aid to facilitate the formation of and/or ensure the retention of a fluid-permeable mass or bed of solids. Thereafter, the sludge and a mixture of two different solvents are charged to an extraction unit where they mix to extract organic material from the refinery sludge. In a final stage, the refinery sludge solid residue from which organic material has been extracted is separated from solvents and organic material, preferably using a mechanical separation means such as filtration, centrifugation, hydrocycloning or settling. The process also includes an optional metal fixation process requiring the addition of commercially available silica or silicate-bearing solutions, fly ash, sodium sulfide, Pozzalime.TM., and the like which is blended with the sludge solids at up to 100% by weight in order to fix the metals in the sludge in an insoluble form.
The '983 process specifies that two solvents are necessary. The first and second organic solvents used in the '983 patent's extraction process are described in very general terms. The first organic solvent can be any aromatic or aromatic-rich solvent that is readily available from a refinery system (such as reformate) or a middle distillate (such as fuel oil, straight run distillates, diesel oil, kerosene) and natural gas condensate. The second organic solvent, specified as different than the first organic solvent, must be of low viscosity and preferably aliphatic, aromatic or cycloaliphatic hydrocarbon having from about 2 to about 9 carbon atoms. The solvent can be a mixture of hydrocarbon compounds, or substantially hydrocarbon compounds having from 3 to about 5 carbon atoms. Liquified petroleum gas (LPG) is specified as a useful second organic solvent, as is commercial propane, butane, propane-butane mixture, special duty propane and propane HD-5, straight run gasoline, and any mixtures of the foregoing solvents.
The process of the U.S. Pat. No. 5,092,983 is limited to the use of solvent extraction with two specified solvents. The method requires a first solvent extraction stage that requires additional solvent extraction apparatus and uses two specific solvents followed by a subsequent stage that requires additional apparatus for separating solvents and extracted organic materials from solid residue. Further, there is no teaching or suggestion of how to perform the step of separating solids from liquids and routing the solids to disposal without exposing workers or the environment to the contents of the extraction and separation vessels. Finally, although it is represented that the solids may be disposed of using "conventional solids disposal techniques (e.g., landfill, etc.)," the process is only asserted to reduce the level of extractable organic material to a level of less than about 1% by weight, based on the weight of the solids. Such a high level of organic material residue in the solids may not meet Best Demonstrated Available Technology (BDAT) requirements and would not meet the Total Petroleum Hydrocarbon Limits (TPH) set by state regulatory agencies to allow the solids to be disposed of in non-hazardous solid waste landfills.
There are other known solvent extraction systems in industry. For example, the BEST 115R process by Resource Conservation Co. utilizes a reusable solvent, triethylamine, which is soluble in both oil and water in low temperatures but soluble only in oil at higher temperatures. In the BEST solvent extraction process, the sludge is fed into an extraction stage, cooled below 40.degree. F. and extracted with triethylamine. The solids are then separated by filtration from the oil/water triethylamine mixture. The separated solids are dried, stripped of residual solvents to meet the EPA-required BDAT for disposal in a hazardous waste landfill. The oil/water/solvent mixture is heated above 130.degree. F. so that the triethylamine becomes insoluble in water and enters the oil phase. The water is then decanted and stripped of any residual triethylamine before being discharged to the refinery waste and the oil is separated from the triethylamine so that the triethylamine can be recycled for use as solvent and the oil is presumably recovered and routed back to the refinery for further processing.
CF System treats oily sludge and utilizes propane as the feed solvent under conditions of agitation to extract oil from the solids in the waste/sludge. In a final step, hot water is used to displace and evaporate residual propane from the propane treated solids.
A horizontal plate-type filter is manufactured by Sparkler Filters, Inc. of Conroe, Texas. The Sparkler filter vessel includes a plurality of plates which may be horizontally disposed during normal filtering operation and then rotated through 90.degree. to vertical positions for discharge of collected cake. The cake is discharged by gravity into the bottom of the filter vessel which contains a rotatable screw or scroll for moving the residue solids outwardly of the vessel. The complete cycle of operation of the filter vessel (filtration and cake discharge) is performed without opening the vessel. However, to the knowledge of the present inventors, this type of Sparkler filter has never been used in the oil refinery environment for any purpose.
What is yet needed is a process for the treatment of oily sludges that can be integrated into a typical oil refinery process scheme. Thus, the process should use solvents available in oil refineries that separates an oil fraction from the oily sludge that can be recycled for reprocessing in the oil refinery to produce a saleable product. Further, separated sludge solids should meet all the U.S. EPA and State requirements for disposal in a non-hazardous solid waste landfill to minimize disposal costs, or at least meet requirements for disposal in a hazardous waste landfill rather than requiring expensive incineration procedures. Finally, the process should desirably be carried out in an enclosed processing system using the minimum amount of vessels to minimize capital investment in equipment. The enclosed processing system should also avoid exposure of labor and the environment to any hazardous or potentially material that may be present in the oily sludge or solvents used in the process.